1. Technical Field
The invention relates to an image forming apparatus.
2. Related Art
In related art, as for the image forming apparatus, there is known, for example, an image forming apparatus having four image forming parts corresponding to respective colors of yellow, magenta, cyan and black, where respective toner images of yellow, magenta, cyan and black are sequentially formed on the photoreceptor drums of those four image forming parts, the toner images of respective colors formed on these photoreceptor drums are primarily transferred in a superposed manner onto an intermediate transfer belt, and the toner images of respective colors are en bloc secondarily transferred onto a recording sheet from the intermediate transfer belt and at the same time, fixed thereon to form a color image.
For controlling the image density in each image forming part of yellow, magenta, cyan or black, the image forming apparatus above is configured such that a patch by a density detection toner image is formed on the photoreceptor drum in each image forming part, the density detection patch formed on each photoreceptor drum is transferred onto an intermediate transfer belt, the density of the density detection patch transferred onto the intermediate transfer belt is detected by a density detection unit, and the image density in each image forming part is controlled according to the detection results of the density detection unit.
In the image forming apparatus above, at the time of forming an image detection patch on the photoreceptor drum in each image forming part of yellow, magenta, cyan or black, when the formation position for the density detection patch in the circumferential direction on the photoreceptor drum is fluctuated, the variation or the like of photosensitive characteristics along the circumferential direction of the photoreceptor drum sometimes affects the density.
Accordingly, in the related-art image forming apparatus, the formation position for the density detection patch on the photoreceptor drum is set to always become the same position, and the density detection patch formed at the same position on the photoreceptor drum is transferred onto the intermediate transfer belt and detected with an attempt to realize the stability of image density and each color.